A. Field of the Invention
Concepts described herein relate generally to data caching, and more particularly, to optimizing disk accesses in a wide area network optimization device.
B. Description of Related Art
Geographically distributed entities, such as a business with multiple local offices in different locations, frequently desire to maintain a logically unified proprietary network that is accessible by all of the geographically distributed entities. To accomplish this, a wide area network (WAN) may be used to link the different locations.
Information technology (IT) managers within geographically distributed entities face the conflicting requirements of keeping costs in check while providing users with new and faster applications. This conflict is most acute on the WAN, where costs can be high and getting applications to perform well is hampered by limited bandwidth and high latency.
Solutions are known to help improve performance over the WAN portion of a network. These solutions may be based on a number of technologies, including data compression, data prefetching and caching, application-specific acceleration, and policy-based bandwidth allocation.
Data caching and compression, in particular, can be used to reduce the perceived latency (response time) of data being accessed over a WAN. Compression and caching techniques may be disk-based, as opposed to semiconductor memory based, due to the orders-of-magnitude larger storage capacity of typical hard disk drives. One known problem with disk-based techniques is that a disk access can be relatively slow, particularly if the disk access requires seeking the disk head to the correct location on the disk platter. Therefore, a data caching or compression technique that encounters a lot of “seeky” disk access sequences (i.e., when the compression patterns or cached objects are dispersed over the disk platter) may spend a relatively large amount of time seeking the disk head to the relevant data instead of reading it.